AC compressor clutch not engaging
 

The clutch on the compressor sometimes engages only for a few seconds and then releases, other times it doesn't engage at all. I unplugged the connector at the compressor and it's getting 12V and there is continuity to ground on the compressor side. I've never worked on AC other than adding freon and checking pressure switches. Is this likely to be a bad compressor? Any help will be appreciated.

Re: AC compressor clutch not engaging
 

You didn't mention the compressor design, so I'm assuming you have an original factory type A-6 compressor.

As the compressor ages, the friction faces wear away. This causes the gap between the two to widen. As it widens, the magnetic field isn't strong enough to overcome the wide gap. If the clutch plate and pulley friction face isn't overly worn and uneven, the gap can be closed by removing shims located on the shaft under the clutch plate. A special puller must be used to remove the clutch plate. The complete clutch can be removed without disturbing the freon charge. It's been years since I've worked on one of those factory compressors and my memory isn't good enough to remember the proper gap dimension, but I think .012" - .015" should work just fine.

The factory Chassis Overhaul Manual contains all the information pertaining to AC compressor repairs.

Re: AC compressor clutch not engaging
 

I don't know the compressor type. Full disclosure; this is not on a gm truck. It's on a foreign made tractor but I was hoping the function was the same. I'm dealing with this as I recover from covid. I'll get info on the compressor when I get a chance. I went to check the connections and when I started it up the compressor was spinning and the ac was blowing cool. I started doing some work and after about 20 minutes I noticed the air wasn't as cool so I popped the hood and the compressor was spinning but it looked to be turning at about half speed. I'm going to do more research to see if the clutch can be replaced or repaired. Thanks again for the help.

PS: The compressor is Valeo DKV11C .

Re: AC compressor clutch not engaging
 

No or too low freon equals no or short clutch engagement.
Double check belt tension. Normally belt slippage is fairly noisy but possible a foreign tractor came with silent belts? Or you have a oil leak somewhere and the belt is too wet to make noise.

The old A-6 and A-4 GM compressors could have their clutches replaced while on the vehicle and without draining the freon. No clue on yours.

Re: AC compressor clutch not engaging
 

We need to know how the freon system is designed on his tractor. Some systems have a suction throttling device that controls the amount of freon pumped by the compressor. On this design, the compressor doesn't cycle off and on, rather, it runs all the time. This is how the compressor operates from the factory on our 68 - 72 trucks. Cycling clutch designs cycle the compressor off and on to control the amount of freon flow and will "short cycle" in the event of low freon.

The OP stated he has checked for voltage at the compressor. I assumed (could be an error on my part) he meant the voltage was present when the clutch was not engaged. That information led me to my diagnosis of a clutch gap issue. The proper way to check voltage at the clutch is to leave the plug connected and probe the connector while the AC is operating.

Re: AC compressor clutch not engaging
 

I used the tractor all afternoon Saturday. I took a can of freon and my voltmeter with me but it worked great all afternoon. I guess it just needed to run a little. I'm sure it'll happen again, and it will be at the most inconvenient and hot time, but I'm happy for the time being. Thanks for all the responses.